不同pH溶液对粉煤灰中溶解性有机质光谱特征的影响

Influence of different pH solutions on spectral characteristics of dissolved organic matter in coal fly ash

为揭示粉煤灰中溶解性有机质(DOM)的组成与性质,采用SEM,XRF,XRD表征粉煤灰理化性质,并考察不同pH(3.01~10.84)条件下粉煤灰中溶出DOM的紫外-可见(UV-vis)吸收光谱与三维荧光光谱(EEMs)特征。结果表明:UV-vis吸收光谱参数E_(2)/E_(3),E_(2)/E_(4),E_(3)/E_(4)随pH升高逐渐降低,DOM相对分子质量、分子缩合度、腐殖化程度随pH升高逐渐增大;DOC的质量浓度随pH升高呈W型变化,其质量浓度变化范围为5.63 mg/L~9.94 mg/L;SUVA260和SUVA280在pH为4.87时取最大值,说明此条件下芳香性强的疏水组分含量最高,荧光区域积分分析显示蛋白类物质(区域Ⅰ+区域Ⅱ)所占比例最高,两个区域所占比例平均值达到58.88%;紫外区类富里酸(区域Ⅲ)随pH升高呈先降低后升高的趋势,区域Ⅳ与区域Ⅴ的物质变化不显著;荧光光谱参数(荧光指数、生物源指数、腐殖化指数、新鲜度指数)显示DOM来源于粉煤灰释放,降低pH有利于新生成DOM,升高pH将增强腐殖质特征;平行因子分析获得3种组分,包括类富里酸及复杂有机化合物;光谱参数相关性分析表明,升高pH将导致DOM相对分子质量增大、自生源贡献降低,且酪氨酸(区域Ⅰ)与紫外区类富里酸(区域Ⅲ)可以发生相互转化。

This study aimed to further investigate the composition and properties of dissolved organic matter(DOM)in coal fly ash.To achieve this,physical and chemical properties of coal fly ash were examined using scanning electron microscope(SEM),X-ray fluorescence spec-troscopy(XRF),and X-ray diffraction(XRD)analyses.Additionally,the effects of pH values ranging from 3.01 to 10.84 on changes in DOM in the coal fly ash solution were investigated using ultraviolet-visible spectrum and three-dimensional fluorescence spectrum techniques.The results indicate that the UV-vis spectral parameters(E_(2)/E_(3),E_(2)/E_(4),and E_(3)/E_(4))of DOM de-crease gradually as the pH increased from 3.01 to 10.84.Meanwhile,the relative molecular weight,polymerization degree,and humification degree increase rapidly with increasing pH.The effect of different pH values on the organic carbon concentration(DOC)exhibits a W-shaped de-pendence,with values ranging from 5.63 mg/L to 9.94 mg/L.Notably,the maximum values of SUVA_(260) and SUVA_(280) are observed at pH 4.78,indicating that hydrophobic members reach their highest level.The results of fluorescence region integral analysis show that the aromatic protein(region Ⅰ+Ⅱ)comprises the highest percentage of total DOM,accounting for approximately 58.88% of the total.The content of fulvic-like acid in the ultraviolet(region Ⅲ)exhibits an ini-tial decrease followed by an increase with increasing pH,while the changes in regions Ⅳ and Ⅴ are not significant.Furthermore,the fluorescence spectral parameter(fluorescence index,bio-logical index,humification index,β∶α)analysis reveal that the DOM primarily originates from coal fly ash emissions,and increasing the pH leads to a decrease in newly generated DOM,while humification characteristics are enhanced.Three fluorescent components,including fulvic-like acid and complex organic compounds,were identified by using PARAFAC models.In addition,the correlation analysis of spectral parameters suggests that increasing pH can result in an in-crease in the relative molecular weight of DOM,a decrease in endogenous characteristic,and the transformation of most fulvic-like acid(region Ⅰ)into forms of tyrosine(region Ⅲ)in water.Overall,studying the spectral characteristics of DOM in fly ash under different pH conditions can provide important theoretical support for further investigation of the dynamic migration and transformation of DOM,as well as changes in the carbon cycle.